The ultimate goal of this project is to improve the result of chemotherapy in acute nonlymphocytic leukemia by the development and appropriate utilization of clinically relevant in vitro leukemic clonogenic assay and chemotherapy sensitivity-testing system for individual patients with acute nonlymphocytic leukemia. The most important specific aim of this project is to utilize the leukemic clonogenic assay, which has been recently developed, in a prospecive randomized fashion as a decision-aiding tool either to/or not to administer a second-line chemotherapy, mitoxantrone, to patients with refractory acute nonlymphocytic leukemia. The benefit obtained by the patients will be assessed by the achievement of complete remission as well as the prolongation of survival. Therefore this will determine/establish whether this in vitro system can be used to improve the treatment of patients with acute nonlymphocytic leukemia. Also efforts will continuously be made to improve the assay itself and chemotherapy-testing method. All the clinical and cell-culture data will be computerized for rapid and accurate storage, retrieval computation and analysis, and also efficient feed-back of cell-culture data to the clinical investigators.